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CONSUMER ELECTRONICS

Optical bonding materials selection guide

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Why choose Dow Performance Silicones?Dow Performance Silicones has been a global leader in silicone-based technology for more than

70 years. Headquartered in Michigan, USA, we maintain manufacturing sites, sales and customer

service offices, and research and development labs in every major geographic market worldwide to

ensure you receive fast, reliable support for your processing and application development needs.

Unique product technologyOur substantial silicone legacy – showcased though the DOWSIL™ and SILASTIC™ brand names that encompass more than 7,000 silicone products and services – offers a portfolio with breadth and proven performance that few companies can match.

Extensive know-howWe multiply our product value with deep in-house expertise and an extended network of industry resources.

Collaborative cultureWe work closely with you to help reduce time and cost at every stage of your new-product development.

StabilityFor more than seven decades, we have been a global leader, investing in manufacturing and quality to help fuel your innovations, through a consistent supply of proven silicone products.

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Key characteristics of DOWSIL™ VE Series silicone optical bonding materials

We’ve tailored DOWSIL™ VE Series silicone optical bonding materials to meet your needs for cost, packaging, and a wide range of attributes – many of which are specific to optically clear resin (OCR) applications.

• High optical transparency

• High thermal stability

• Stable to UV degradation

Our DOWSIL™ VE Series bonding materials – which offer the inherent benefits of silicone – are available with a broad range of viscosities and mechanical properties. These materials provide:

• Good yellowing resistance under use conditions

• Good elongation

• Aging reliability

• Low modulus (to eliminate the mura effect)

• Choices for adhesion, hardness, viscosity, and refractive index

• A range of cure times and cure technologies

Potential uses and applications • Automotive displays

• Consumer displays requiring reliability in harsh conditions, such as micro/mini LED displays

DOWSIL™ VE Series silicone optical bonding for displays

Applications for optical bonding

Cover window (glass or plastic)

Touch sensor Display cell/panel

DOWSIL™ VE Series optical bonding material

Benefits of optical bonding • Improved viewing experience and readability

• Increased display ruggedness

• Extended display product life

Unlike most displays, those used in automotive interiors endure harsh environmental conditions, including extreme temperatures, high humidity, and prolonged UV exposure. They consequently demand more robust adhesive materials that still support simple, cost-effective processing.

The DOWSIL™ VE Series offers UV cure, UV/thermal dual- cure and thermal-cure systems. These solutions are silicone-based optically clear resins that reliably bond a variety of cover window materials – including glass, PMMA, and PC – to automotive LCD display modules. Their excellent optical properties help displays deliver superb performance properties, such as high transmittance, low haze, minimal yellowing, and superior reliability under common automotive environment test conditions.

These silicone OCR solutions adapt easily to incumbent optical bonding processes and deliver superior photothermal stability, mechanical properties, and optical performance for optimized processing and performance of your next automotive display design.

Why silicone optical bonding materials from Dow?The inherent versatility of silicone chemistry can help expand your design freedom, increase your processing options, and enhance the performance and reliability of your device. As a class of materials, silicones generally offer demonstrable benefits over organic-based solutions.

Dow builds on silicone’s inherent potential by combining it with industry-leading materials knowledge, application expertise, customer collaboration, and a global footprint.

We’ve designed this guide to help you quickly narrow your search for a bonding solution that will meet your specific application demands.

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DOWSIL™ VE Series optical bonding materials – UV-cure technology

DOWSIL™ VE-6001 UV_T Optical Bonding Material

DOWSIL™ VE-2530 UV Optical Bonding Material

DOWSIL™ VE-6520 Optical Bonding Material(2)

Form factor 1-part 1-part 1-partProduct properties, uncuredMix ratio, A:B — — —Viscosity, Part A, mPa·s — — —Viscosity, Part B, mPa·s — — —Viscosity, Mixed, mPa·s 3,600 28,000 25,000

Pot life @ RT, min3 months without UV exposure

>1 week under dark >1 week under dark

Cure conditions>4,000 mJ/cm² metal halide UV LED at 395, 405 nm

>4,000 mJ/cm² metal halide UV LED at 395, 405 nm

>2,000 mJ/cm2 at 365nm: B-stageFull cure 24hr at 25°CFull cure 20min at 60°C

Product properties, curedHardness 54 Shore 00 60 Shore 00 20 Shore AVolume shrinkage, % <1.0 <1.0 <1.0Lap shear strength(1), kgf/cm2 8.3 10.0 8.3Transmittance, % >99 >99 >99Refractive index 1.53 1.53 1.41Yellowness index(1) 0.32 0.26 0.28Optical properties after 1,000 hours at 65°C/95% RHYellowness index(1) — 0.55 —Optical properties after 1,000 hours at 85°C/85% RHYellowness index(1) 1.1 — 0.52

(1)Silicone thickness: 200 µm, glass/glass. | (2)Developmental material. | Specification writers: These values are not intended for use in preparing specifications. Please contact your local Dow representative or sales office before writing specifications on these products.

DOWSIL™ VE-6001 UV_T Optical Bonding MaterialOptical properties after reliability test Sandwiched glass with 200 µm thickness, metal halide D bulb at 4,000 mJ/cm2

0 200 400 600 800 1,00090

92

96

94

98

100

T% a

t 550

nm

Time, hr

At 85°C/85% RHAt TCAt 105°CAt -40°CPer ASTM G154

0

0.2

0.4

0.6

0.8

1

0 200 400 600 800 1,000

b*

Time, hr



0 200 400 600 800 1,0000

0.5

1.5

1

2

2.5

3

Yello

wne

ss in

dex

Time, hr

Volu

me

shrin

kage

, %

DOWSIL™ VE-6001 UV_T Optical Bonding Material

0%

1%

2%

3%

4%

5%

Acrylic OCR

Transmittance at 550 nm

b*

Yellowness

Volume

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DOWSIL™ VE Series optical bonding materials – thermal-cure technology

DOWSIL™ VE-5002 H Optical Bonding Material

DOWSIL™ VE-1204 Quick Cure Optical Bonding Material(2)

DOWSIL™ VE-1204 H Optical Bonding Material(2)

DOWSIL™ VE-1303 H Optical Bonding Material(2)

Form factor 2-part 2-part 2-part 2-part

Product properties, uncured

Mix ratio, A:B 1:1 1:1 1:1 1:1

Viscosity, Part A, mPa·s 350 3,800 4,000 2,700

Viscosity, Part B, mPa·s 264 3,900 4,000 2,800

Viscosity, Mixed, mPa·s 315 3,900 4,000 2,800

Pot life @ RT, min <360 3.5 <60 3.0

Cure conditions 1 hr @ 60°C 1 hr @ 25°C 1 hr @ 60°C 0.5 hr @ 40°C

Product properties, cured

Hardness 21 Shore 00 40 Penetration 40 Penetration 45 Penetration

Volume shrinkage, % <1.0 <1.0 <1.0 <1.0

Lap shear strength(1), kgf/cm2 6.9 5.7 6.1 3.6

Transmittance, % >99 >99 >99 >99

Refractive index 1.41 1.41 1.41 1.54

Yellowness index(1) 0.3 0.3 0.3 0.3

Optical properties after 1,000 hours at 85°C/85% RH

Yellowness index(1) 0.5 0.5 0.6 0.5

(1)Silicone thickness: 200 µm, glass/glass. | (2)Developmental material. | Specification writers: These values are not intended for use in preparing specifications. Please contact your local Dow representative or sales office before writing specifications on these products.

DOWSIL™ VE-1204 Quick Cure Optical Bonding MaterialOptical properties after reliability test Sandwiched glass with 200 µm thickness, 1 hr @ 25°C

Transmittance at 550 nm b*

Yellowness

0 200 400 600 800 1,00090

92

96

94

98

100

T% a

t 550

nm

Time, hr

Per ASTM G154

At 85°C/85% RHAt TCAt 105°CAt -40°C

0 200 400 600 800 1,0000

0.2

0.6

0.4

0.8

10.0

b*

Time, hr

Per ASTM G154


0 200 400 600 800 1,0000

1.0

0.5

2.0

1.5

2.53.0

Yello

wne

ss in

dex

Time, hr

Per ASTM G154


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Selecting an optical bonding material

Typical-size display (~6" to ~ 13") Slit-coating process Using precure process Fill material: Large process window for precure condition

Dam material: Same as fill material with spot-cure system

Large precure process window material

Flowable-viscosity OCR products

Proper-wettability OCR products

Flowable-viscosity OCR products

High-thixotropy OCR products

High-viscosity OCR products

With dam process

Dam cure process window

For 10"+ size filling

Pattern design

For thicker layer (~400 µm)

For thinner layer (~350 µm)

Dam and fill process

Patterning process

Screen-printing process

Specific-design display - Curved display - 3D auto display

Fill material: Large process window for precure condition




Slit-coating process Using precure process

With dam process

For thicker layer (~400 µm)


Screen-printing process

Large-size display (~20") Slit-coating process

Screen-printing process For thicker layer (~400 µm)

With dam process

Using precure process Fill material: Large process window for precure condition




Low-viscosity product for fill material

High-viscosity with thixotropic product for dam material


With dam processInjection process

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Optical bonding with silicones

Cover glass

OCR

OCR

LCM

Touch sensor

8

Materials requirements for various process options

Liquid optical bonding technology was introduced in late 1970s in the liquid crystal display (LCD) industry and has been in use ever since. In the 2010s, optical bonding technology was being used widely due to the low total cost of ownership compared with the dry-bonding process.

The liquid optical bonding process can use either one-part UV-cure materials or two-part thermal-cure materials. The one-part materials, known as UV cure OCR or LOCA, are compatible with most bonding equipment and have faster cure times and easier handling than two-part materials, making them the material of choice for many optical bonding companies.

There are three different liquid optical bonding processes: the dam and fill process, patterning, and the slit-coating process. In 2015, screen (stencil) printing processes and dam and injecting processes had been newly proposed for specific display designs, such as curved displays, 3D design displays, notch-design displays, and others. DOWSIL™ VE Series optical bonding materials are proven to be processable with a wide range of optical bonding processes. Five representative liquid optical bonding processes are illustrated on the next page.

Typical processes for optical bonding

Sto

rag

e m

od

ulus

, Pa

Injectionmaterial

105

104

100 1,000 10,000

Specific-design display Curved or 3D auto display application

Display (~6" to ~13")Typical auto display application

Large-size display (~20")Especially for digital information displays

Dam material

Screen-printing material

Viscosity, mPa·s

Fill,patterningslit-coating

material

8

9

LCD module

Cover window

Dispense OCR on module and precure it for DAM

Dispense OCR on cover window and

laminate cover glass

Laminate glass and precure the material

Full cure

Dispense OCR on cover window

Laminate cover window on LCD

Materials spread Full cure (side cure added

if needed)

LCD module

Cover window

Slit-coat OCR on cover window

UV precure Laminate cover window and precure the material

Full cure

LCD moduleCover window

Dam and fill

Slit-coating

Patterning

Injection

Cover window

Dispense dam material on LCD module

Laminate cover glass on LCD

Inject OCR into laminated LCD with cover window

Full cure (side cure added if needed)

LCD module

Mask

Cover window

Dispense OCR on mask frame to coat specific area

Print OCR with squeegee blade

Laminate cover window and LCD

Full cure

Screen printing

Dam and injecting

4

5

1

2

3

Representative optical bonding processes

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Environmental reliability test conditions in the automotive industry have become more challenging in recent years, with even more stringent conditions proposed in 2016. Consider the newly proposed reliability test conditions:

• 105°C for the high-temperature degradation test

• 85% RH or 90% RH at 85°C for the humid heat constant test

• -40 to ~95°C for the thermal shock test and QUV or QSUN tests

To meet these exacting standards, increasingly reliable OCR materials are required for automotive displays. Acrylic OCR materials and other organic-film materials have demonstrated weaknesses in their ability to meet these proposed reliability requirements.

During the reliability tests based on the newly proposed conditions, various failure modes could be generated in optical bonding layers and films. Key factors to prevent failures include changing the bonding process and/or changing the OCR and film materials.

Typical failure modes

Bubbles Polarizer discoloration

Display and touch-sensing area

Flexible PCB for display and touch-sensing

Mura

Generated by the lamination process and outgassing

Generated by the chemical reaction in PVA

DelaminationCaused by volume shrinkage and adhesion change

YellowingTypical chemical reliability issue in the optical material industry

Caused by mechanical stress changes and bonding material color changes

Black matrix

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Chemical method

1. Use wire to debond touch sensor and LCD module.

2. Spray solvent (IPA or MICSOL 1620) on residual adhesives, or cloth wipe covering residual adhesives.

3. Wait five minutes until residual adhesives soften.

4. Rub with plastic blade to remove residual adhesives.

5. Spray with solvent and clean with cloth wipe.

Reworkability methods for optical coupling resins (OCR)

Mechanical method

1. Use wire to debond touch sensor and LCD module.2. Store substrate with residual adhesives below -25ºC for 30 minutes.3. Rub with plastic blade to remove residual adhesives.4. Spray with solvent (IPA or MICSOL 1620) and clean with cloth wipe.

Samples cleaned with IPA and

MICSOL 1620

WireSolvent

Solvent

Cloth wipe

Plastic blade

Softened residual adhesives

OCRLCD module OCR

LCD module

or

OCRLCD module

After rubbing with plastic blade

After cleaning with solvent (IPA or MICSOL 1620)

IPA MICSOL 1620

Mark from wire removal

Touch sensor OCR or OCA LCD module

Wire

Touch sensor OCR or OCA LCD module

Store below -25°C OCRLCD module

Plastic blade

Softened residual adhesives

OCRLCD module

We bring more than just an industry-leading portfolio of advanced silicone-based materials. As your dedicated innovation leader, we bring proven process and application expertise, a network of technical experts, a reliable global supply base, and world-class customer service.

To find out how we can support your applications, visit dow.com/electronics.

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NOTICE: No freedom from infringement of any patent owned by Dow or others is to be inferred. Because use conditions and applicable laws may differ from one location to another and may change with time, Customer is responsible for determining whether products and the information in this document are appropriate for Customer’s use and for ensuring that Customer’s workplace and disposal practices are in compliance with applicable laws and other government enactments. The product shown in this literature may not be available for sale and/or available in all geographies where Dow is represented. The claims made may not have been approved for use in all countries. Dow assumes no obligation or liability for the information in this document. References to “Dow” or the “Company” mean the Dow legal entity selling the products to Customer unless otherwise expressly noted. NO WARRANTIES ARE GIVEN; ALL IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED.

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